Set aside your idea to build one by hand for the moment.
In my area, the local Nurseries have wishing wells. They have wind mills and even wooden, hand-operated well pumps! You may find that the price is right just to buy something. And they come in all different sizes.
I, like me, you live near Amish country, there are a lot of ideas at the handi-craft shops they run. (Just another thought.)
Now, about finding plans, you may not have the tools to do the job. Of course, you may need a saw. But you'll probably need a miter box / power-miter, a lathe, and/or some clamps. Soooo, by the time you buy or borrow these few things, you might find it more economical to have bought one that's pre-made. BUT, I'm sure there are KITS you can buy that have all the wood pre-cut. Then, it's a simple matter of putting the puzzel together (and only having a good, working knowledge of how to follow directions written in 8 different languages!) BEFORE you order any plans, find out what TOOLS you'll need to build one!
Here's just one link from the WEB. There are a lot more with free and for FEE plans. (Others may post them.) You need to 'chop' at the Location FIeld in your Browser to get to the Home Page. From there, you can 'contact' the mfgr.